 /*******************************************************************************
  * Copyright (c) 2000, 2005 IBM Corporation and others.
  * All rights reserved. This program and the accompanying materials
  * are made available under the terms of the Eclipse Public License v1.0
  * which accompanies this distribution, and is available at
  * http://www.eclipse.org/legal/epl-v10.html
  *
  * Contributors:
  * IBM Corporation - initial API and implementation
  *******************************************************************************/
 package org.eclipse.core.internal.variables;


 /**
  * Local version of org.eclipse.jface.util.ListenerList (modified)s
  */
 public class ListenerList {
     /**
      * The current number of listeners.
      * Maintains invariant: 0 <= fSize <= listeners.length.
      */
     private int fSize;

     /**
      * The list of listeners. Initially <code>null</code> but initialized
      * to an array of size capacity the first time a listener is added.
      * Maintains invariant: listeners != null if and only if fSize != 0
      */
     private Object [] fListeners= null;

     /**
      * The empty array singleton instance, returned by getListeners()
      * when size == 0.
      */
     private static final Object [] EmptyArray= new Object [0];

     /**
      * Creates a listener list with the given initial capacity.
      *
      * @param capacity the number of listeners which this list can initially accept
      * without growing its internal representation; must be at least 1
      */
     public ListenerList(int capacity) {
         if (capacity < 1) {
             throw new IllegalArgumentException ();
         }
         fListeners= new Object [capacity];
         fSize= 0;
     }

     /**
      * Adds a listener to the list.
      * Has no effect if an identical listener is already registered.
      *
      * @param listener a listener
      */
     public synchronized void add(Object listener) {
         if (listener == null) {
             throw new IllegalArgumentException ();
         }
         // check for duplicates using identity
 for (int i= 0; i < fSize; ++i) {
             if (fListeners[i] == listener) {
                 return;
             }
         }
         // grow array if necessary
 if (fSize == fListeners.length) {
             Object [] temp= new Object [(fSize * 2) + 1];
             System.arraycopy(fListeners, 0, temp, 0, fSize);
             fListeners= temp;
         }
         fListeners[fSize++]= listener;
     }

     /**
      * Returns an array containing all the registered listeners.
      * The resulting array is unaffected by subsequent adds or removes.
      * If there are no listeners registered, the result is an empty array
      * singleton instance (no garbage is created).
      * Use this method when notifying listeners, so that any modifications
      * to the listener list during the notification will have no effect on the
      * notification itself.
      */
     public synchronized Object [] getListeners() {
         if (fSize == 0) {
             return EmptyArray;
         }
         Object [] result= new Object [fSize];
         System.arraycopy(fListeners, 0, result, 0, fSize);
         return result;
     }

     /**
      * Removes a listener from the list.
      * Has no effect if an identical listener was not already registered.
      *
      * @param listener a listener
      */
     public synchronized void remove(Object listener) {
         if (listener == null) {
             throw new IllegalArgumentException ();
         }

         for (int i= 0; i < fSize; ++i) {
             if (fListeners[i] == listener) {
                 if (--fSize == 0) {
                     fListeners= new Object [1];
                 } else {
                     if (i < fSize) {
                         fListeners[i]= fListeners[fSize];
                     }
                     fListeners[fSize]= null;
                 }
                 return;
             }
         }
     }

     /**
      * Removes all the listeners from the list.
      */
     public void removeAll() {
         fListeners= new Object [0];
         fSize= 0;
     }

     /**
      * Returns the number of registered listeners
      *
      * @return the number of registered listeners
      */
     public int size() {
         return fSize;
     }
 }


